Crossed field microwave device

ABSTRACT

A traveling wave crossed field device is disclosed having dual sets of spaced conductive cathode electrode segments in parallel electrically with one set cooperating as a control element and the remaining set performing primarily as the emitter. Discrete electron cycloidal trajectories are considered in arriving at the spacing between adjacent elements. The cathode configuration provides for space charge control throughout the entire interaction region. Additionally, high- Mu switching, as well as high-speed shutoff characteristics, has been achieved by means of very low-control voltage requirements.

United States Patent Dudley et al. 1 Feb. 29, 1972 [54] CROSSED FIELD MICROWAVE DEVICE 3,207,946 9/1965 l-laus et al ..3l5/39.3 [72] lnventors: Kenneth W. Dudley, Sudbury; George H. sag 315/39 3 MacMaster waltham both of Mass- [73] Assignee: Raytheon Company, Lexington, Mass. Primary Examiner-Eli Lieberman Assistant Examiner-Saxfield Chatmon, Jr. [221 F11ed= June Attorney-Harold A. Murphy, Joseph D. Pannone and Edgar 21 Appl. No.: 42,180 ROM [57] ABSTRACT [52] [1.8. CL ..3l5/3.5, 315/393, 315/3973,

313/338, 330/42 313/89 A traveling wave crossed field device is disclosed having dual [51] Int. Cl. ..H0lj 25/34 Sets of Spaced conducuve cathode electrode segments m [58] Field of Search ..315 3.5 x, 39.3, 39.63, 5.1 1, Parallel electrically m "i a 3l5/5'12, 3973; 330/42, 43; 331/89; 313/338 merit and the remaining set performing pnmanly as the emitter. Discrete electron cycloidal tra ectones are con- [56] References Cited sidered in arriving at the spacing between adjacent elements. The cathode configuration provides for space charge control UNITED STATES PATENTS throughout the entire interaction region. Additionally, high-[L switching, as well as high-speed shutoff characteristics, has gemstem been achieved by means of very low-control voltage requirerown mems. 3,458,753 7/1969 Staats.... .....313/338 X 3,278,791 10/1966 Favre ....315/39.3 X 10 Claims, 12 Drawing Figures PATENTEnmzsmz 3,646,388

SHEET 3 [IF 4 CROSSED FIELD MRCROWAVE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to cathodes for crossed field microwave devices.

2. Description of the Prior Art In the applicable devices the principle of interaction between an electron beam launched from a cathode source with the electromagnetic wave fields of traveling waves propagated by a slow wave structure is utilized. The combined fields of the propagated energy may be resolved into space harmonic waves having varying phase velocities. The electron beam velocity is synchronized with the phase velocity of a desired space hannonic component to result in amplification and/or oscillation of high frequency RF energy.

A member of the foregoing class includes the M-type oscillator or amplifier having mutually perpendicular unidirectional electric and magnetic fields in the region where the electron beam is directed along an interaction path defined adjacent to the slow wave propagating structure. Substantially high-power microwave energy has been generated in very efficient structures referred to as the Amplitron" which comprises a circular but nonreentrant slow wave propagating structure terminated at its ends by matched impedances to provide operation over the frequency region of interest. A reentrant electron beam originating from a continuously emissive-coated cathode member is spaced from and concentrically disposed with the slow wave structure. A DC potential is applied between the cathode and slow wave structure or anode. A magnetic field is applied parallel to the axis of the cathode member and transverse to the electric field. In operation, the Amplitron provides properties substantially similar to the conventional backward wave oscillators where the electron beam interacts with a backward wave spatial harmonic. Such devices conventionally employ thermionically controlled cathode members which imposes a requirement for additional circuitry to supply the necessary thermionic heater operating potentials, as well as serious operational life disadvantages due to the deposition of evaporated emissive material on adjacent electrode structures to thereby result in loss of primary emission capability, as well as seriously affecting the electrical characteristics of such structures. Further particulars regarding prior art devices of a high-power capability may be had by referring to U.S. Pat. No. 2,859,411 issued Nov. 4, 1958 to W. C. Brown and US. Pat. No. 2,977,502 issued Mar. 28, 1961 to W. C. Brown and Edward C. Dench. An advantage of such devices in contradistinction with other types of crossed field tubes such as a magnetron is that a change of applied voltage to the anode slow wave structure primarily increases the power output instead of changing the velocity of the adjacent electron beam. Efficiencies in the order of 70-75 percent are attainable and many thousands of watts and megawatts of power will be yielded.

Present day expanding requirements for sophistication in radar systems have resulted in the use of new techniques requiring pulse burst modes where the pulse width and repetition rates are varied over short intervals. Such pulsed applications require fast rise time and fall, as well as pulse groups not readily available with conventional discharging line-type highpower modulators. In addition, multitube chains such as those employed in phased array radar systems have pulsing requirements for precise, simultaneous switching of many amplifiers. The Amplitron traveling wave device due to its high-efficiency and high-power capabilities can provide some of the characteristics of the new pulse requirements if rapid switching of pulses can be achieved with low additional voltage supply requirements and sharp rise time with a minimum of jitter and noise. One prior art solution involves the use of a single wide control segment over a portion of the large circular cathode occupying approximately a 40 sector electrically insulated from the remaining structure and controlled by a separate supply voltage. Upon rendering of the control electrode positive with respect to the remaining emissive portion the electrons in the interaction region will be removed by brute force upon reaching the area of the control electrode. Since the applicable traveling wave devices are conventionally of circular configuration and provide a substantial radius at the highpower levels desired, electrons in the interaction region will be required to traverse many RF cycles before being removed from the interaction region. As a result, prior art control electrode techniques for the rapid switching of high-power amplifiers and/or oscillators are completely unsatisfactory. A need arises, therefore, for a cathode structure which will not only provide rapid switching with relatively low voltages but preferably, will incorporate self-modulation and thereby eliminate the need for high-power modulating supplies.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention a reentrant beam of electrons is provided by a unique cathode electrode to interact with traveling waves on an adjacent slow wave propagating structure. The cathode incorporates individualized sets of cathode segments with adjacent segments having selectively varying electrical properties. The segments may be disposed in an interdigital arrangement with alternate segments being electrically connected in parallel. By suitable means one set of segments may be rendered nonemitting to thereby prevent further emission from the cathode and thereby provide control means for a total cathode current shutoff and cessation of operation of the device.

Under the new concept of the invention the advantages of a cathode electrode having a high secondary emissive material are utilized. An initiating RF trigger pulse on a nonreentrant slow wave propagating structure results in the generation of free electrons and gas molecules in the interaction region which pick up energy from the RF field and bombard the cathode material to release a profusion of secondary electrons. These secondary electrons form the electron beam directed within the interaction region. Cathode materials having a secondary emission ratio in excess of unity are preferred. The absence of direct or indirect thermionic means simplifies tube construction and obviates the necessity for additional cathode heater voltage supplies. No current, therefore, will be drawn from the tube with operating voltages applied until the high-power RF pulse is transmitted along the slow wave propagating structure within the envelope.

In accordance with one embodiment of the invention a cathode electrode is provided with having first and second sets of interdigital cathode segments mutually isolated with alternate segments electrically in parallel. The spacing between the adjacent members will be sufficient to approximate one cycloid of an electron trajectory. By varying the applied electrical potential a substantially small value (1 KV or less) between the two sets the cathode electrode will perform as a highor low-operating secondary emitter in devices having as high as 30 KV applied as an operating potential across the interaction region. In this manner the traveling wave tube may be switched on or off with a relatively low-voltage control. It is also permissible to vary the selection of materials for alternate cathode segment members so that one, or the control set, has a secondary electron emission ratio of less than unity. The alternate cathode segment members will then be selected of a material having a high secondary electron emission ratio in excess of unity to primarily perform the emitter function of the cathode electrode. By biasing the lower secondary electron emissive material control set slightly positive with respect to the emitter set of segments collection of electrons will rapidly take place at alternate segments and prevent buildup of the space charge in the interaction region. The space charge will thereby be swept out of the region at numerous intervals separated by approximately I cycloid of the electron travel. Consequently, the device can be turned off very rapidly with the electrons traveling relatively few RF cycles before collection. The tube will then be rendered operative by another RF trigger pulse along the input terminal of the slow wave propagating structure.

Ideally, the tube can be self-modulating using solely RF keying pulses. Operation of the tube would commence when the RF drive is applied and cease when the drive signal stops. A constant DC anode voltage would be on the tube at all times.

Embodiments of the invention have demonstrated effective switching at power levels well in excess of I KW with good gain and efficiency. The device operating at anode-cathode potentials of 30 KV can be switched as rapidly within nanoseconds by applying a relatively low DC control pulse of l KV or less. This results in a highi switch value of 30 compared to conventional prior art brute force collector electrodes which provide values of only 3-5. The term ii" employed in this description is defined as the ratio of anode voltage to control voltage.

The development of the new switching techniques considering the discrete electron cycloid trajectories will result in very rapid switching with very low-voltage requirements. A reduction in modulating voltage requirements over the prior art by an order of magnitude will result in significant savings and result in enhanced utilization of large high-power amplifier tube chains in industrial heating, communication and phased array radar systems.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details for the provision of illustrative embodiments, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, wherein:

FIG. I is a vertical cross-sectional view of the illustrative embodiment of the invention;

FIG. 2 is a perspective view of onehalf of the cathode electrode member of the invention;

FIG. 3 is a perspective view of both halves of the cathode electrode interdigital embodiment of the invention;

FIG. 4 is an enlarged detailed cross-sectional view taken along the line 44 in FIG. 1;

FIG. 5 is a view taken along the line 5-5 in FIG. 1;

FIG. 6 is a vertical cross-sectional view of an alternative embodiment of a cathode electrode embodying the invention;

FIG. 7 is a view taken along the line 77 in FIG. 6;

FIG. 8 is a diagrammatic representation of the inphase electron trajectories along a portion of the interaction path;

FIG. 9 is a diagrammatic representation of the out-of-phase electron trajectories;

FIG. 10 is a diagrammatic representation of the embodiment of the invention in a traveling wave device with both cathode electrode segments at the same potential;

FIG. I1 is a diagrammatic representation of the embodiment of the invention in a traveling wave device with one set of cathode electrode segments biased slightly negative with respect to the remaining set; and

FIG. 12 is a diagrammatic representation of the embodiment of the invention in a traveling wave device with the control set of cathode electrode segments biased positively with respect to the remaining set.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings the illustrative traveling wave device 10 is of a cylindrical configuration housing within envelope 11 a slow wave propagating structure 12 and a concentrically spaced cathode assembly 13 defining with the propagating structure an interaction region 114. An electric field is applied transversely between the cathode electrode assembly 13 and the slow wave propagating structure 12 across the interaction region. A magnetic field extends mutually perpendicular to the electric field and parallel to the longitudinal axis of the cathode electrode. A magnet assembly 15 includes a pair of pole piece members 16 and 17 together with abutting C-shaped magnets 18 and I9. Additional inner magnetic pole pieces 24 and 25 are included within the tapered section of the cathode sleeve members 22 and 23, as shown in greater detail in FIG. 4.

Envelope 11 comprises cylindrical body member 26 together with upper plate member 27 and lower plate member 28 which are hermetically sealed to provide an evacuated atmosphere within the envelope. The slow wave propagating structure 12 includes a plurality of spaced substantially U- shaped anode elements 29 in a circular array which are brazed or otherwise affixed to a coolant manifold support structure 30 secured to the inner wall surfaces of the body member 26. The slow wave elements may be made hollow to communicate with passages 31 in the manifold member 30 for circulation of a coolant. A pair of straps 32 and 33 connect alternate elements 29 as indicated in greater detail in FIG. 5. The overall slow wave propagating structure 12 is of the electrically nonreentrant type with the severed strap members connected to plural impedance matched RF input and output terminal conductors 34 and 35. A source of high frequency energy is propagated through waveguide transmission line section 36 which may be of the ridged type having opposing ridges 37 and 38 secured to the opposing broad walls. A septum (not shown) is conventionally disposed between the terminal ends of the slow wave delay line structure to electrically isolate the input and output terminals 34,35. The waveguide transmission line section 36 is accommodated within a slot in the envelope body member 26 and the ends of the transmission line are hermetically sealed thereto to preserve the evacuated condition. Terminal conductors 34 and 35 extend from the slow wave straps and are secured to the ridge members 37 and 38. The techniques for the matching of the characteristic impedance of the slow wave propagating structure to the RF transmission line are well known in the microwave art and need not be further elaborated on in this description. Energy from a suitable high-power source (not shown) is supplied to the waveguide transmission line to provide the RF driver pulse signal directed along input terminals 35 through the traveling wave tube slow wave propagating structure to the output ter minals 34 in a counterclockwise manner while the reentrant electron beam is clockwise as indicated by the arrow. The device may also be operated as an oscillator wherein a locking signal is applied to the input terminals in lieu of a signal to be amplified and the oscillatory energy generated within the tube will be coupled through the output terminals to a suitable utilization load.

Referring now to FIGS. 2 and 3 along with FIGS. 4 and 5 the details of the cathode electrode assembly 13 of the invention will now be described. Cathode sleeve assembly members 22 and 23 extend axially within the envelope II and are provided with tapered apex sections 20 and 21. The inner ends of the cathode sleeve members are provided with an interdigital array of elongated vertical segment members 39 and 40. The respective cathode sleeve members are electrically isolated from each other in order that individual biasing potentials may be applied to the respective cathode segment members. In FIG. 2 a circular array of, illustratively, eight cathode segments is shown although in numerous exemplary embodiments larger numbers of such segments may be provided as, for example, in FIG. 5 wherein a total of 22 cathode electrode segments are provided by the interdigital sets of II members each. The cathode segment members are secured to collar members 41 and 4-2 and may be solid or hollow to provide for an internal cooling arrangement hereinafter to be described. The cathode segment members 39 and 40 are illustrated as cylinders and may be fabricated of emitter materials having a predetermined secondary electron emission ratio. In one embodiment of the invention cathode segment members 39 are provided of a material such as titanium which has a secondary electron ratio value of less than unity and generally a value of between 0.40 to 0.85 over a range of voltages up to 600 electron volts. This set of cathode segment members will be referred to as the control set in view of the lower secondary emission ratio value, as well as electrical biasing arrangements hereinafter to be described.

The opposing interdigital set of cathode segment members 40 may desirably be fabricated utilizing cylinders of a material having a high secondary emission ratio such as, for example, platinum having values well in excess of unity and as high as 1.8 over a range of from 400 to 4,000 electron volts. This set of cathode segments will be referred to, therefore, as the emitter set.

FIG. 3 illustrates cathode assembly 13 comprising alternate titanium 39 and platinum 40 cathode segments adjacent to one another and electrically isolated. The effective secondary emission ratio value of the combined members is controlled by the application of individual voltages from sources 43 and M to the cathode segment sets determined by the desired cycle of operation of the traveling wave device. The provision of a plurality of cathode segments along the interaction region at spaced intervals with means for providing varying electrical properties provides an effective means for switching of the high power traveling wave device with very low-control voltage requirements. For maximum efficiency the spacing between cathode segments 39 and 40 is selected to approximate one cycloid of electron travel along the circumferential path within the interaction region 14.

Referring next to FIGS. 4 and 5 the details of an illustrative embodiment of the invention incorporating secondary electron emissive cylindrical cathode segment members adapted to permit passage of fluid coolant means will now be described. Cathode sleeve members 22 and 23 have tapered portions and 21 together with collar members 41 and 42 at the apex. The cathode segment cylinders 39 and 40 in the cir cular array are disposed in the interdigital arrangement. Each of the cathode segment cylinders 39 and 40 are provided with an inner tubulation 45 and 46 through which a fluid coolant may be introduced. Further, the ends are sealed by means of plugs 47 and 48. The sets of cathode segments are supported in the desired array with the alignment carefully controlled by means of central disc members 49 and 50. The central disc members are aligned by means of dielectric rod members 51 and 52 joined to the respective disc members to also maintain the electrical isolation. Central apertures 53 and 54 are provided in the disc members for insertion of additional alignment members. It is understood that the individual cylindrical cathode segment members are affixed to the supporting collar members 41 and 42 as well as the disc members by wellknown brazing techniques.

Central hollow tubulations 55 and 56 extend within each of cathode sleeve members 22 and 23 and are supported adjacent the inner ends by means of partition members 57 and 58 to define a manifold arrangement for the direction of the fluid coolant means throughout the cathode segment array. Each supporting structure for the cathode electrode sets is provided with an outer sleeve member 22 which also channels the returning fluid coolant to a combined inlet and outlet connector 60 at the outer end of the inner sleeve members. The respective conductive members of the cathode supporting structure are biased at the appropriate DC potential in the conventional manner and the outer cylinder 59 is preferably of a dielectric material.

As previously noted, the slow wave electrode structure may also be cooled by means of introduction of a fluid coolant in jacket member 34) and passageways 31 for circulation throughout the array of hollow U-shaped anode elements.

In a similar manner the individual sets of cathode segments are cooled by means of the introduction of a fluid coolant from connector 69 through tubulations 55 and 56 into passageways 61 and 62 which communicate with each of the respective hollow cylindrical cathode segment members 39 and 40. The egress movement of the fluid coolant will be through the axial tubulations 45 and do within each of the cathode segment members in the direction of fluid passageways 63 and 64 defined between the cathode sleeve member portions 20,22 and 2l,23 and the internal pole piece members 24 and 25. Beyond the pole piece members a rather large volume-handling area is provided by reason of the relatively large diameters of the cathode sleeve members 22 and in N65. 6 and 7 an alternative embodiment of the cathode electrode assembly is illustrated. A cylindrical conductive body member 65, illustratively from a low secondary emission material, such as titanium, is provided along its peripheral circumferential edges with a plurality of splines 66. The splines are spaced apart to define slots 67 and the spacings are, again, the distance of one cycloid of electron travel. Slots 67 may be provided with a radius adjacent the joining edges of the bottom and sidewalls to provide for enhanced electrical properties. in the illustrative example 12 slots are provided in the body member to thereby define the 12 spline members 66. Within each of the slots, then, the remaining set of cylindrical cathode segment members 68 are positioned to thereby provide an interdigital array similar to that previously disclosed utilizing two complete sets of individual cathode segment members. The composition of the members 63 may illustratively be of a higher secondary electron emission material, such as platinum. The combined electrode assembly will provide the desired emission properties and be operated in substantially the same manner as the embodiment illustrated in FIGS. 1-5 inclusive.

Referring next to FIGS. 8 and 9 a discussion of the operation of the embodiment of the invention follows. For the sake of clarity a continuous type cold cathode member 69 is illustrated and the slow wave propagating structure anode members are designated by numeral 70. The appropriate electrical signs are noted in the illustration. The spaced cathode and anode members define therebetween an interaction region 71 through which the electron beam is directed.

As the electrons leave the cathode 69 they encounter a force towards the slow wave structure indicated by the arrow 72 designated Edc. A force perpendicular to the velocity of the electrons will also be exerted because of the magnetic field as indicated by the circle 73. in addition, a varying force exists indicated by the arrow 74 and symbol Erf due to the high frequency electric fields of the traveling waves propagated along slow wave structure 7%. The electrons which are in proper phase with respect to these high frequency electric fields transfer energy from the applied DC field to die RF field and continue traversing in a cycloidal trajectory toward the slow wave structure as indicated by the path 75. The electrons, however, which are not in proper phase will extract energy from the RF field and be returned to the cathode 69. The trajectory of such out-of-phase electrons is, therefore, indicated by the cycloidal trajectory path 76 in lFlG. 9. These electrons bombard the cathode approximately one-half RF cycle after launch and thereby generate secondary electrons indicated by the arrows 77. Part of these secondaries will be emitted inphase with the radiofrequency fields and continue on to the slow wave propagating structure. Other secondary electrons will be emitted out-of-phase and will return to the cathode again to create further secondary electrons. In this manner the electron beam within the interaction region 71 is created. The circumferential distance traveled around the cathode during a cycle is about one-half the distance between the spokes of the electron space charge which will form in the interaction region.

in accordance with the concepts of the present invention and referring next to lFlGS. lid-l2 inclusive the cathode assembly comprises a plurality of segment members of a vertical cylindrical configuration in an interdigital array with the distance between each adjacent member being approximately I cycloid of electron travel. The alternate segment members are electrically connected in parallel. The members 39 designate the socalled control set and are of a secondary emissive material having a lower ratio value. Hence, by providing varying electrical properties by material or varying potential means, the control set of cathode members are rendered nonemitting and the total cathode current will be shut off to make the tube inoperative. The cathode members designated 39 in the illustration, therefore, can represent cylindrical members of titanium while the members 40 are of the higher secondary emissive material, namely, platinum.

In the situation depicted in H6. ill both the cathode electrode members 39 and 40 are biased at approximately the same potential. The tube in this situation should operate normally at low-power levels and the resultant current may be at a lower value due to the lower combined effective emission ratio. The trajectories of the electrons initiating from the members 39 and 40 are indicated by the paths 82 and each alternate more highly emissive material will provide a greater profusion of secondary electrons which in turn will traverse the circumferential interaction region.

In the next possible combination, the so-called control set of cathode members is made slightly negative with respect to the remaining set, say by a value of, for example, i KV or less which results in the operative situation depicted in FIG. ill. All the bombarding electrons from members 39 will bombard the high secondary emitter 40 at values of about 1,000 electron volts as indicated by the trajectory paths 78 and 79. Due to the electrical difi'erences very few electrons will gain sufficient energy to strike and will thereby form a cusp near the next member 39 and continue around with the space charge spoke to bombard the next high secondary emitter 40 and create a profusion of secondary electrons indicated by the arrows 80. In this mode of operation the control set of cathode segment members 39 will have little or no effect on the tube operation and the electrons will see and bombard the highly secondary electron emissive platinum members 40.

Referring next to FIG. 12 the control set of cathode members 39 are now biased slightly positive with respect to the adjacent cathode members by approximately 1 KV or less. In this mode of operation all the bombarding electrons will hit the members 39 but due to the low secondary emissive properties relatively few secondary electrons will be emitted. These secondaries will have an average potential energy of about 1,000 electron volts above the high secondary emission set of cathode members. As a result, most of these electrons cannot extract enough energy from the RF field to bombard the main cathode emitting set. The trajectory indicated by the curve 81, therefore, reveals that the secondary electrons will not bombard the highly emissive members 40 and will be absorbed eventually by the next control set of member 39. The effective secondary emission ratio of the overall cathode will, therefore, be very low, possibly, in the region of 0.6, so that the available cathode current will rapidly fall to zero in a very few RF cycles. This mode of operation will result in the shutdown of the tube operation.

In the fabrication of the respective cathode segment members in the illustrative embodiment it is possible to fabricate the titanium members by evaporation over a copper tubing base. The remaining cathode segment members could then be fabricated of a platinum tubing. in the foregoing description the applied DC electric potential between the cathode and slow wave structure was approximately 30 KV and it is, therefore, apparent that with a small control voltage differential of approximately 1 XV or less the device has a very high-p.

switching value in the vicinity of 30.

In the practice of the invention numerous means may be utilized for switching the device on and off. For example, in the foregoing embodiments a low control voltage from a suitable source was supplied to provide a small differential between adjacent sets of cathode members separated by approximately 1 electron cycloid. The switching times observed were in the order of 10 nanoseconds. It was possible in the exemplary embodiment to obtain RF gain with pulses having a width of less than 100 nanoseconds.

The circuit requirements for modulating of a traveling wave device in accordance with the invention will eliminate the need for complex high-power modulators. The device will be simply turned on by means of an RF drive signal pulse with a low-power circuit suitable for applying a minimal additional bias to render the control set positive with respect to the emitter set of cathode members. Alternatively, by suitable adjustment of the magnetic field potential values it will be possible to switch the device on by solely the REF drive signal and turn the device off when the RF drive signal ceases.

Many variations may be practiced by those skilled in the art such as, for example, altering the configuration of the sets of cathode members in a manner befitting any desired electron trajectories. For example, a square cathode member may be preferred disposed adjacent to a cylindrical member. The cathode electrode member also is not limited solely to the cold cathode configuration since it is perfectly permissible to have a cathode actuated by a simple thermionic source disposed in some portion of the circumferential array to thereby initiate operation. Such a cathode electrode assembly, therefore, may be utilized in many different types of amplifier or oscillator devices where low-voltage control is provided by varying the electrical emissive properties of adjacent members of the cathode electrode assembly to thereby provide at numerous intervals along an interaction region means for extinguishing or enhancing emission in order that the tube is rapidly switched on or off. The important value of the invention, however, resides in the response of the electrical space charge in a matter of a relatively few RF cycles to thereby shut off cathode current.

Various modifications and alterations will readily occur to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. it is intended, therefore, that the embodiment shown and described herein be considered as exemplary only and not in a limiting sense.

What is claimed is:

l. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

means for generating and directing electrons along an interaction region adjacent to said propagating means;

said electron generation means including spaced interdigitated emissive cathode members having alternately varying emissive properties during operation of the device;

said cathode members being spaced apart a distance of approximately 1 electron cycloid trajectory throughout the interaction region.

2. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

means for generating and directing a beam of secondary electrons along an interaction region adjacent to said propagating means;

said electron generation means including spaced interdigitated emissive cathode members having alternately varying secondary electron emission characteristics dur ing operation of the device;

said cathode members being spaced apart a distance of approximately l electron cycloid trajectory throughout said interaction region;

and means for biasing alternate members to provide a predetermined electrical voltage differential relative to adjacent cathode members.

3. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

a cathode structure for generating and directing a beam of electrons along a path adjacent to said propagating means;

said cathode structure having first and second sets of mutually electrically isolated interdigitated emissive segment members with alternate segment members biased in parallel electrically;

and means for varying the emissive properties of adjacent members to provide for regulation of total electron beam current during operation of the device.

4. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

a cathode structure for generating and directing a beam of electrons along a path adjacent to said propagating means;

said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate segment members biased in parallel electrically;

the spacing between adjacent members being a distance substantially equal to 1 electron cycloid trajectory;

and means for varying the electron emissive properties of one set of members relative to the remaining set to regulate total electron beam current throughout said path.

5. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

a cathode structure for generating and directing a beam of electrons along an interaction region adjacent to said propagating means;

said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate members in parallel electrically;

the spacing between adjacent members being a distance substantially equal to l electron cycloid trajectory;

one set of said members having varying electron emissive properties relative to the remaining set;

and means for electrically biasing each set at an individualized predetermined voltage potential.

6. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

a cathode structure for generating and directing a beam of electrons along an interaction region adjacent to said propagating means;

said cathode structure having first and second sets of spaced interdigitated segment members with alternate members in parallel electrically;

the spacing between adjacent members being a distance substantially equal to l electron cycloid trajectory;

and means for electrically biasing one set of members at a relatively low positive voltage differential relative to the remaining set to regulate the electron space charge in the interaction region.

7. A traveling wave device comprising:

means for propagating electromagnetic wave energy;

a cold cathode structure adapted to be energized by high frequency traveling waves to yield a beam of secondary electrons along an interaction region adjacent to said propagation means;

said cathode structure having a first set of segment members of a material having low secondary electron emissive properties and a second set of segment members of a material having a substantially high secondary electron emissive properties;

said sets of cathode segment members being electrically isolated from one another and being spatially disposed in an ill secondary electron emissive properties of the first set member material is less than unity and the second set member material is in excess of unity with a combined emissive property in the 10 order of 0.6.

9. A crossed field electron discharge device comprising:

a slow wave structure having an input energy terminal at one end;

means for supplying high frequency electromagnetic energy to said input terminal;

a concentrically disposed cathode structure for generating and directing a beam of electrons along an interaction region defined with said slow wave structure;

said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate members in parallel electrically;

means for electrically biasing said members to vary the electron emissive characteristics and regulate the operation of the device; and means for producing crossed electric and magnetic fields in the region between said cathode and slow wave structures.

10. A crossed field electron discharge device comprising:

a nonreentrant slow wave structure having an input terminal at one end;

means for supplying high frequency electromagnetic energy to said input terminal;

a cold cathode structure for generating a reentrant beam of secondary electrons along a path adjacent to said slow wave structure to interact in energy exchanging relation with said input energy;

said cathode structure having first and second sets of interdigitated emissive segment members with alternate members in parallel electrically and being spaced apart a distance of approximately 1 electron cycloid trajectory;

said first set comprising members having lower secondary electron emissive properties relative to second set;

means for biasing the first set of members at an electrical voltage differential relative to the second set sufficient to regulate the electron beam current and operation of the device;

and means for producing crossed electric and magnetic fields throughout the interaction path. 

1. A traveling wave device comprising: means for propagating electromagnetic wave energy; means for generating and directing electrons along an interaction region adjacent to said propagating means; said electron generation means including spaced interdigitated emissive cathode members having alternately varying emissive properties during operation of the device; said cathode members being spaced apart a distance of approximately 1 electron cycloid trajectory throughout the interaction region.
 2. A traveling wave device comprising: means for propagating electromagnetic wave energy; means for generating and directing a beam of secondary electrons along an interaction region adjacent to said propagating means; said electron generation means including spaced interdigitated emissive cathode members having alternately varying secondary electron emission characteristics during operation of the device; said cathode members being spaced apart a distance of approximately 1 electron cycloid trajectory throughout said interaction region; and means for biasing alternate members to provide a predetermined electrical voltage differential relative to adjacent cathode members.
 3. A traveling wave device comprising: means for propagating electromagnetic wave energy; a cathode structure for generating and directing a beam of electrons along a path adjacent to said propagating means; said cathode structure having first and second sets of mutually electrically isolated interdigitated emissive segment members with alternate segment members biased in parallel electrically; and means for varying the emissive properties of adjacent members to provide for regulation of total electron beam current during operation of the device.
 4. A traveling wave device comprising: means for propagating electromagnetic wave energy; a cathode structure for generating and directing a beam of electrons along a path adjacent to said propagating means; said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate segment members biased in parallel electrically; the spacing between adjacent members being a distance substantially equal to 1 electron cycloid trajectory; and means for varying the electron emissive properties of one set of members relative to the remaining set to regulate total electron beam current throughout said path.
 5. A traveling wave device comprising: means for propagating electromagnetic wave energy; a cathode structure for generating and directing a beam of electrons along an interaction region adjacent to said propagating means; said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate members in parallel electrically; the spacing between adjacent members being a distance substantially equal to 1 electron cycloid trajectory; one set of said members having varying electron emissive properties relative to the remaining set; and means for electrically biasing each set at an individualized predetermined voltage potential.
 6. A traveling wave device comprising: means for propagating Electromagnetic wave energy; a cathode structure for generating and directing a beam of electrons along an interaction region adjacent to said propagating means; said cathode structure having first and second sets of spaced interdigitated segment members with alternate members in parallel electrically; the spacing between adjacent members being a distance substantially equal to 1 electron cycloid trajectory; and means for electrically biasing one set of members at a relatively low positive voltage differential relative to the remaining set to regulate the electron space charge in the interaction region.
 7. A traveling wave device comprising: means for propagating electromagnetic wave energy; a cold cathode structure adapted to be energized by high frequency traveling waves to yield a beam of secondary electrons along an interaction region adjacent to said propagation means; said cathode structure having a first set of segment members of a material having low secondary electron emissive properties and a second set of segment members of a material having a substantially high secondary electron emissive properties; said sets of cathode segment members being electrically isolated from one another and being spatially disposed in an interdigital array at intervals substantially equal to 1 electron cycloid trajectory; and means for electrically biasing said first set of members at a voltage differential sufficient to regulate secondary electron emission throughout the interaction region.
 8. A traveling device according to claim 7 wherein the secondary electron emissive properties of the first set member material is less than unity and the second set member material is in excess of unity with a combined emissive property in the order of 0.6.
 9. A crossed field electron discharge device comprising: a slow wave structure having an input energy terminal at one end; means for supplying high frequency electromagnetic energy to said input terminal; a concentrically disposed cathode structure for generating and directing a beam of electrons along an interaction region defined with said slow wave structure; said cathode structure having first and second sets of spaced interdigitated emissive segment members with alternate members in parallel electrically; means for electrically biasing said members to vary the electron emissive characteristics and regulate the operation of the device; and means for producing crossed electric and magnetic fields in the region between said cathode and slow wave structures.
 10. A crossed field electron discharge device comprising: a nonreentrant slow wave structure having an input terminal at one end; means for supplying high frequency electromagnetic energy to said input terminal; a cold cathode structure for generating a reentrant beam of secondary electrons along a path adjacent to said slow wave structure to interact in energy exchanging relation with said input energy; said cathode structure having first and second sets of interdigitated emissive segment members with alternate members in parallel electrically and being spaced apart a distance of approximately 1 electron cycloid trajectory; said first set comprising members having lower secondary electron emissive properties relative to second set; means for biasing the first set of members at an electrical voltage differential relative to the second set sufficient to regulate the electron beam current and operation of the device; and means for producing crossed electric and magnetic fields throughout the interaction path. 